1. Field of the Invention
The present invention relates generally to an image forming apparatus and, more particularly, to a system and method for reducing the churning of toner in the image forming apparatus.
2. Description of the Related Art
An image forming apparatus, such as a color printer typically includes four image forming stations associated with four colors, black, magenta, cyan, and yellow. Each image forming station includes a laser to expose a latent image on the charged surface of a photoconductive drum. The latent image on each photoconductive drum is developed with the appropriate color toner and is then transferred to either an intermediate transfer medium or directly to a media (such as paper) that travels past the photoconductive drums. The un-fused toner on the media is then fused to the media by application of heat and pressure in a fuser assembly.
In the process of printing a sequence of pages, the image forming station runs for a short time before printing the first page (run in) and runs for a short period of time after printing the last page (run out). The run in and run out processes are required to prepare the various components of the image forming station before printing and to clean the image forming station after completion of printing, respectively. When a print job includes a small number of pages, the overhead time consumed during run in and run out is more than the time required for actual printing of the pages. Excessive amount of time spent during run in and run out results in a degradation of print quality due to recycling of toner in the image forming stations of the image forming apparatus. Toner that is not used in the printing process is re-circulated many times before it is used for printing. This repeated recycling of the toner is known as churn and results in print quality defects such as starvation, grainy print, and poor transfer to the media.
In the image forming apparatus, the photoconductive drums that print each color are arranged in tandem and typically all the photoconductive drums start rotating at the same time. This is done to provide a stable motion quality of the photoconductive drums within the image forming apparatus, however since the upstream image forming stations are used before the downstream stations, the downstream stations experience toner churn that is not productive at the beginning of a print job. Similarly during the completion of the print job, the upstream stations experience toner churn until the downstream station complete the image transfer process.
Further, the photoconductive drum transfers its image to an intermediate transfer member that accumulates the images from each of the four imaging forming stations. The intermediate transfer member then transfers the accumulated image to a media at a second transfer point. In the prior art system, the photoconductive drums continue to rotate until the intermediate transfer member completes transfer of the image to the media at the second transfer point. This linkage between the running of the photoconductive drums and the intermediate transfer member is done to improve motion quality and reduce slippage that might cause damage to the photoconductive drums or the intermediate transfer member. However, this process also results in toner churn that is undesirable.
Therefore, it is desirable to increase the useful life of the image forming apparatus by reducing excess toner churn.